The chronometer from the Greek "chronos"(time) and the Latin "metrum" (to measure) is a navigational instrument used to determine longitude. It was invented in the early 18th C and was essential to navigation until radiotelegraphy was invented in the 20th C. Despite the use of GSN-GPS at the end of the 20th C its presence on board is still obligatory.
The 19th C chronometer in its round brass case and its mahogany box is highly prized by collectors